Semiconductor devices are typically fabricated on a substrate that provides mechanical support for the device and often contributes to the electrical performance of the device as well. Silicon, germanium, gallium arsenide, sapphire and silicon carbide are some of the materials commonly used as substrates for semiconductor devices. Many other materials are also used as substrates. Semiconductor device manufacturing typically involves fabrication of many semiconductor devices on a single substrate.
Substrates are often formed in the shape of circular wafers having a diameter presently ranging, for example, from less than 1 inch (2.54 cm) to over 12 inches (30.5 cm) depending on the type of material involved. Other shapes such as for example square, rectangular or triangular wafers exist. Semiconductor devices are formed on the wafers by the precise formation of thin layers of semiconductor, insulator and metal materials which are deposited and patterned to form useful semiconductor devices such as diodes, transistors, solar cells and other devices.
Semiconductor crystals can be produced by a number of techniques. For example, in a typical silicon carbide crystal growth technique, a seed crystal and a source material are both placed in a reaction crucible which is heated to the sublimation temperature of the source and in a manner that produces a thermal gradient between the source and the marginally cooler seed crystal. The thermal gradient encourages vapor phase movement of the materials from the source to the seed followed by condensation upon the seed and the resulting bulk crystal growth. The method is also referred to as physical vapor transport.
A bulk single crystal of semiconductor material may then be desirably cut into wafers and polished prior to the growth of epitaxial layers and the formation of devices on the wafers as described above. Mechanical polishing can leave defects, such as scratches in a wafer, which in turn may cause defects in the epitaxial layers. Defects from mechanical polishing can be reduced with additional treatment, for example a reactive ion etch (RIE).